It is, of course, well known to provide a container for chilling materials such as food or the like, which includes maintaining perishable articles in a chilled condition, where the containers operate independently of outside energy sources. This is particularly true of containers which are designed to be portable. Such devices are known in various embodiments and for use in various sets of circumstances, particularly transportable containers such as are used in the transportation of goods such as by rail and air transport. With the use of a suitable chilling agent, e.g., solidified carbon dioxide, commonly known as "dry ice", in such containers, the material to be chilled can be held for a considerable length of time below the temperature of the ambient environment. Such containers are also used to carry prepared meals and supplies of food stuffs for service to air or rail passengers. In such cases, Departments of Health commonly require that the meals or food stuffs for service are maintained within a certain temperature range until just before serving.
The manner of operation of such containers for chilled goods resides in the fact that the dry ice, which is generally used as the cooling agent, vaporizes or sublimes upon contact with the heat from surrounding atmosphere or from the container, and that the cold gas resulting therefrom, which is heavier than air, is carried by the effect of gravity into the tank which contains the material to be chilled. Thus, so long as the dry ice supply lasts, the transfer of heat into the container can be entirely or at least partially controlled and compensated for by the insulated walls of the container.
In a known container for such material, the inside chamber is subdivided into a cooling agent part to carry the cooling agent and a chilled material part for the storage of the chilled material, and the cooling agent part is found directly below the cover of the container. However, since the cooling agent part is only insufficiently insulated from the outside, the sublimation or vaporization heat of the dry ice is drawn for the most part from the environment and, thus, the chilled goods are not so effectively chilled. Since the sublimation heat from dry ice can have a more extensive cooling effect than the cold carbon dioxide gases arising therefrom, the losses are great with such known containers and they have a low degree of thermal effect and also the cooling effect is not uniform in the chamber containing the material to be chilled and preserved. Indeed, in those regions closest to the cooling agent, the material can be excessively cooled.